Disclosing a premeditated intent not to fly the itinerary fully as ticketed could provide a ground for AZ to send you a bill after the fact. And a rather substantial one at that, I'd reckon, given the difference between the prevailing one-way business class fare from YYZ-MXP and the fare you actually paid.

Improbable? Perhaps.

But not impossible.

I wouldn't risk telling AZ. Using your ticket to maximize its value to you by skipping some inconvenient or unncessary flight(s)? Fine idea. There are some, I'm sure, who might have missed a connection or two on the back end of their journey for one reason or another.